1. Nuclear Chemistry Chapter 25

2. Introduction to Nuclear Chemistry • Nuclear chemistry is the study of the structure of and the they undergo. atomic nuclei changes

3. Chemical vs. Nuclear Reactions

4. Chemical vs. Nuclear Reactions

5. Chemical vs. Nuclear Reactions

6. Chemical vs. Nuclear Reactions

7. Chemical vs. Nuclear Reactions

8. The Discovery of Radioactivity (1895 – 1898): Roentgen • found that invisible rays were emitted when electrons bombarded the surface of certain materials. • Becquerel accidently discovered that phosphorescent salts produced spontaneous emissions that darkened photographic plates uranium

9. The Discovery of Radioactivity (1895 – 1898): Marie Curie • isolated the components ( atoms) emitting the rays • – process by which particles give off • – the penetrating rays and particles by a radioactive source uranium Radioactivity rays Radiation emitted

10. The Discovery of Radioactivity (1895 – 1898): polonium • identified 2 new elements, and on the basis of their radioactivity • These findings Dalton’s theory of indivisible atoms. radium contradicted

11. The Discovery of Radioactivity (1895 – 1898): same Isotopes • – atoms of the element with different numbers of • – isotopes of atoms with nuclei (too / neutrons) • – when unstable nuclei energy by emitting to attain more atomic configurations ( process) neutrons Radioisotopes unstable many few Radioactive decay radiation lose stable spontaneous

12. Alpha radiation • Composition – Alpha particles, same as helium nuclei • Symbol – Helium nuclei, He, α • Charge – 2+ • Mass (amu) – 4 • Approximate energy – 5 MeV • Penetrating power – low (0.05 mm body tissue) • Shielding – paper, clothing 4 2

13. Beta radiation • Composition – Beta particles, same as an electron • Symbol – e-, β • Charge – 1- • Mass (amu) – 1/1837 (practically 0) • Approximate energy – 0.05 – 1 MeV • Penetrating power – moderate (4 mm body tissue) • Shielding – metal foil

14. Gamma radiation • Composition – High-energy electromagnetic radiation • Symbol – γ • Charge – 0 • Mass (amu) – 0 • Approximate energy – 1 MeV • Penetrating power – high (penetrates body easily) • Shielding – lead, concrete

15. Review of Atomic Structure

16. Review of Atomic Structure

17. Review of Atomic Structure

18. Review of Atomic Structure

19. Chemical Symbols • A chemical symbol looks like… • To find the number of , subtract the from the mass # 14 C atomic # 6 neutrons mass # atomic #

20. Nuclear Stability not • Isotope is completely stable if the nucleus will spontaneously . • Elements with atomic #s to are . • ratio of protons:neutrons ( ) • Example: Carbon – 12 has protons and neutrons decompose 1 20 very stable p+:n0 1:1 6 6

21. Nuclear Stability 21 82 • Elements with atomic #s to are . • ratio of protons:neutrons (p+ : n0) • Example: Mercury – 200 has protons and neutrons marginally stable 1:1.5 80 120

22. Nuclear Stability unstable > 82 • Elements with atomic #s are and . • Examples: and radioactive Uranium Plutonium

23. Alpha Decay α • Alpha decay – emission of an alpha particle ( ), denoted by the symbol , because an α has 2 protons and 2 neutrons, just like the He nucleus. Charge is because of the 2 . • Alpha decay causes the number to decrease by and the number to decrease by . • determines the element. All nuclear equations are . He 4 2 protons +2 mass 4 atomic 2 Atomic number balanced

24. Alpha Decay • Example 1: Write the nuclear equation for the radioactive decay of polonium – 210 by alpha emission. Step 1: Write the element that you are starting with. Step 2: Draw the arrow. Mass # Pb 210 4 206 He Po 84 2 82 Atomic # Step 3: Write the alpha particle. Step 4: Determine the other product (ensuring everything is balanced).

25. Alpha Decay • Example 2: Write the nuclear equation for the radioactive decay of radium – 226 by alpha emission. Mass # 226 4 222 He Ra Rn 88 2 86 Atomic #

27. Beta decay β • Beta decay – emission of a beta particle ( ), a fast moving , denoted by the symbol or . β has insignificant mass ( ) and the charge is because it’s an . • Beta decay causes change in number and causes the number to increase by . electron e- e 0 0 -1 electron -1 no mass atomic 1

28. Beta Decay • Example 1: Write the nuclear equation for the radioactive decay of carbon – 14 by beta emission. Mass # e 14 0 14 C N -1 6 7 Atomic #

29. Beta Decay • Example 2: Write the nuclear equation for the radioactive decay of zirconium – 97 by beta decay. Mass # e 0 97 97 Zr Nb -1 40 41 Atomic #

31. Gamma decay electromagnetic • Gamma rays – high-energy radiation, denoted by the symbol . • γ has no mass ( ) and no charge ( ). Thus, it causes change in or numbers. Gamma rays almost accompany alpha and beta radiation. However, since there is effect on mass number or atomic number, they are usually from nuclear equations. γ 0 0 no mass atomic always no omitted

32. Transmutation Transmutation • – the of one atom of one element to an atom of a different element ( decay is one way that this occurs!) conversion radioactive

33. Review 4 2 0 -1

34. Half-Life half Half-life time • is the required for of a radioisotope’s nuclei to decay into its products. • For any radioisotope,

35. Half-Life

36. Half-Life • For example, suppose you have 10.0 grams of strontium – 90, which has a half life of 29 years. How much will be remaining after x number of years?   • You can use a table:

37. Half-Life • Or an equation! initial mass mt = m0 x (0.5)n mass remaining # of half-lives

38. Half-Life • Example 1: If gallium – 68 has a half-life of 68.3 minutes, how much of a 160.0 mg sample is left after 1 half life? ________ 2 half lives? __________ 3 half lives? __________

39. Half-Life • Example 2: Cobalt – 60, with a half-life of 5 years, is used in cancer radiation treatments. If a hospital purchases a supply of 30.0 g, how much would be left after 15 years? ______________

40. Half-Life • Example 3: Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days? ______________

41. Half-Life • Example 4: The half-life of polonium-218 is 3.0 minutes. If you start with 20.0 g, how long will it take before only 1.25 g remains? ______________

42. Half-Life • Example 5: A sample initially contains 150.0 mg of radon-222. After 11.4 days, the sample contains 18.75 mg of radon-222. Calculate the half-life.

43. Nuclear Reactions • Characteristics: • Isotopes of one element are into isotopes of another element • Contents of the change • amounts of are released changed nucleus energy Large

44. Types of Nuclear Reactions • decay – alpha and beta particles and gamma ray emission • Nuclear - emission of a or Radioactive disintegration proton neutron

45. Nuclear Fission Fission splitting • - of a nucleus • - Very heavy nucleus is split into approximately fragments • - reaction releases several neutrons which more nuclei • - If controlled, energy is released (like in ) Reaction control depends on reducing the of the neutrons (increases the reaction rate) and extra neutrons ( creases the reaction rate). two equal Chain split slowly nuclear reactors speed absorbing de

47. Nuclear Fission • - 1st controlled nuclear reaction in December 1942. 1st uncontrolled nuclear explosion occurred July 1945. • - Examples – atomic bomb, current nuclear power plants

48. Nuclear Fusion combining Fusion • - of a nuclei • - Two nuclei combine to form a heavier nucleus • - Does not occur under standard conditions ( repels ) • - Advantages compared to fission - , • - Disadvantages - requires amount of energy to , difficult to • - Examples – energy output of stars, hydrogen bomb, future nuclear power plants light single + + inexpensive no radioactive waste large start control